Cooling system

ABSTRACT

A cooling system that employs a coolant dispersal subsystem connected to a fluid ejector. The coolant dispersal subsystem is operable to supply liquid coolant to the fluid ejector. The fluid ejector is placed adjacent to a surface to be cooled and operable to eject the liquid coolant onto the surface.

BACKGROUND

[0001] The present invention is directed to cooling a heated surface. More particularly, the invention is directed to a cooling system that utilizes a fluid ejector such as a print head to dispense a liquid coolant.

[0002] A waste product of most, if not all, electronic devices is heat. If the waste heat is not dispersed, the efficiency of the device decreases. Common solutions include the use of heat sinks to absorb waste heat. Often times a heat sink is supplemented by a fan. In hand held and other smaller devices, the use of fans or heat sinks is not an option due to power and size constraints. These devices rely on air flow for cooling. Advances in the miniaturization of electronic components have resulted in smaller devices that generate larger amounts of waste heat. It is predicted that the thermal loads of future microelectronic technologies will exceed the capabilities of traditional air cooling systems.

SUMMARY

[0003] Heat dissipation rates using thin liquid films can be at least two orders of magnitude greater than that achieved through traditional air cooling methods. Accordingly, a cooling system has been invented that employs a coolant dispersal subsystem connected to a fluid ejector. The coolant dispersal subsystem is operable to supply liquid coolant to the fluid ejector. The fluid ejector is placed adjacent to a surface to be cooled and operable to eject the liquid coolant onto the surface.

DESCRIPTION OF THE DRAWINGS

[0004]FIG. 1 is an exploded view of a print head.

[0005]FIG. 2 is a cross sectional view of a print head.

[0006]FIG. 3 is a schematic representation of a cooling system incorporating a fluid ejector according to an embodiment of the present invention.

[0007] FIGS. 4-7 are illustrations of a magnetic drive system for positioning the fluid ejector of FIG. 3 according to an embodiment of the present invention.

[0008]FIG. 8 is a block diagram illustrating the logical components of the control of FIG. 3 according to an embodiment of the present invention.

[0009]FIG. 9 is a schematic representation of a cooling system incorporating an array of fluid ejectors according to an embodiment of the present invention.

[0010]FIG. 10 is a block diagram illustrating the logical components of the controller shown in FIG. 9 according to an embodiment of the present invention.

[0011]FIGS. 11 and 12 are schematic illustrations showing the insertion and removal of a coolant container according to an embodiment of the present invention.

[0012]FIG. 13 is a flow diagram illustrating the operation of the cooling system of FIG. 3 according to an embodiment of the present invention.

[0013]FIG. 14 is a flow diagram illustrating the operation of the cooling system of FIG. 9 according to an embodiment of the present invention.

DETAILED DESCRIPTION

[0014] Introduction:

[0015] A cooling system has been invented that employs a fluid ejector such as a print head to dispense a liquid film over a heated surface. Heat dissipation rates using thin liquid films can be at least two orders of magnitude greater than that achieved through traditional air cooling methods.

[0016]FIG. 1 is an exploded view of a print head 10 traditionally used to disperse ink on a sheet of paper or other print medium. Print head 10 includes substrate 12 on which an array of resistors 14 is formed and orifice plate 16 having orifices 18. Each orifice 18 corresponds to a resistor 14. When orifice plate 16 is placed against substrate 12, each orifice 18 aligns with a resistor 14. The size of a print head is often characterized by the area it can covers in one pass over a sheet of paper. The first generation of print heads included twelve orifices that could cover a one-quarter inch swath. More recent print heads include up to five hundred twelve orifices that can cover a one inch swath.

[0017]FIG. 2 is a cross sectional view of print head 10. Not shown in FIG. 1, is reservoir body 20 which supports a back surface of substrate 12 forming reservoir 22. Reservoir 22 is a cavity used to hold a liquid such as ink, or, in the case of the present invention, a supply of liquid coolant. Substrate 12 includes channel 23, thin film layer or layers 24, barrier layer 26, and body 27. Channel 23 is an opening providing a path for liquid coolant to flow out of reservoir 22 over resistors 14. Thin film layers 24 are materials formed on substrate 12 in or on which resistors 14 are formed. Thin film layers 24 also include various layers of conductive and insulating material used to selectively deliver electrical current to resistors 14. Barrier layer 26 is formed on thin film layers 24 and supplies an attachment surface for orifice plate 16 to form manifold chamber 28 between thin film layers 24 and orifice plate 16.

[0018] Manifold chamber 28 is a cavity for holding liquid coolant between resistors 14 and orifices 18. Channel 23 provides a path between reservoir 22 and manifold chamber 28. Each orifice 18 is aligned with a resistor 14. When energized, a given resistor 14 heats the liquid coolant in manifold chamber 28 to form vapor bubble that ejects a liquid droplet through a corresponding orifice 18.

[0019] Components:

[0020] The components of one embodiment of the invented cooling system will now be described with reference to FIG. 3. FIG. 3 illustrates device 29 having a circuit board 30. Device 29 represents generally any device that generates heat. Circuit board 30 represents the electronic components of device 29 that provide a heated surface to be cooled. The invented cooling system includes a number of subsystems including fluid ejector 10, a coolant dispersal subsystem, a drive subsystem, a temperature sensing subsystem, and a control subsystem. Fluid ejector 10 represents generally structure capable selectively ejecting or dispersing a liquid to form a film on a surface. It is expected that fluid ejector 10 will be a print head. The coolant dispersal subsystem includes container 32, dispenser 34, and distributor 35. Container 32 represents generally any structure having an internal cavity for holding a liquid coolant and an opening through which liquid coolant can exit container 32. Distributor 35 represents generally any structure connecting dispenser 34 to fluid ejector 10 through which a liquid coolant can flow.

[0021] The liquid coolant used can be of varying types. Water is a good choice due to its availability and thermal properties. Water, of course, is also environmentally friendly. However, when using water, the components being cooled must be encapsulated. The 3M Corporation sells a liquid coolant named fluroinert that can be used without requiring encapsulation.

[0022] Dispenser 34 represents generally any structure capable of selectively allowing or causing liquid coolant from within container 32 to flow through distributor 35 to fluid ejector 10. Where, for example, container 32 contains a liquid coolant under pressure, dispenser 34 may be a valve capable of allowing selected quantities of liquid coolant to expel from container 32. Where container 32 is not under pressure, dispenser 34 may be a pump capable of urging liquid coolant out of container 32 through distributor 35 to fluid ejector 10.

[0023] The drive subsystem includes first and second actuators 36 and 37 and first and second axis rails 38 and 40. First actuator 36 represents generally any mechanism capable of urging fluid ejector 10 back and forth along first axis rail 38. Second actuator 37 represents generally any mechanism capable of urging fluid ejector 10, first actuator 36, and first axis rail 38 back and forth parallel to second axis rail 40. As illustrated, first and second axis rails 38 and 40 are perpendicular to one another and define a plane parallel and adjacent to circuit board 30. When used in combination, actuators 36 and 37 are then capable of selectively positioning fluid ejector 10 within that plane.

[0024] The temperature sensing subsystem includes sensor array 42. Circuit board 30 has been partially cut away to illustrate the placement of sensor array 42 adjacent and parallel to both circuit board 30 and the plane across which fluid ejector 10 can travel at the urging of actuators 36 and 37. Sensor array 42 represents a grouping of temperature sensing elements each able to sense the temperature of an adjacent and localized area of circuit board 30. Controller 44 represents generally any combination of hardware and programming capable of performing the following tasks: (1) receiving data representing temperature readings from each element of sensor array 42; (2) directing first and second actuators 36 and 37 to selectively place fluid ejector 10; (3) directing dispenser 34 to allow liquid coolant to flow to fluid ejector 10; and (4) energizing fluid ejector 10 ejecting liquid coolant onto circuit board 30.

[0025] FIGS. 4-7 illustrate an embodiment of the present invention in which actuators 36 and 37 and axis rails 38 and 40 form a magnetic drive capable of selectively placing fluid ejector 10. FIG. 5 is a cross-sectional view of FIG. 4 taken perpendicular to the lengthwise axis of rail 38. FIG. 7 is a cross-sectional view of FIG. 6 taken perpendicular to the lengthwise axis of rail 40.

[0026] Referring first to FIGS. 4 and 5, fluid ejector 10 slides back and forth along first axis rail 38 as a force, having a vector parallel to first axis rail 38, is applied to carriage 46. Carriage 46, which is connected to fluid ejector 10, includes opening 47 through which first axis rail 38 passes. Opening 47 has a shape that generally conforms to the cross sectional shape of first axis rail 38—in this case rectilinear—allowing carriage 46 to slide back and forth along axis rail 38 without rotating around axis rail 38. Carriage 46 includes permanent magnets 48 and 50 that partially, if not completely, surround opening 47. First axis rail 38 includes conductive coil 52 running lengthwise through its center. First actuator 36 then is a device capable of causing an electric current to flow though coil 52 in a selected direction. As current flows through coil 52, a magnetic field is generated that runs lengthwise along first axis rail 38. The direction of that field depends on the direction the current flows through coil 52. The generated magnetic field in conjunction with permanent magnets 48 and 50 result in a force that urges carriage 46 to slide along rail 38 carrying fluid ejector 10. It is expected that rail 38 will be constructed from a materiel that will allow magnets 48 and 50 to hold carriage 46 stationary relative to rail 38 when no current is running through coil 52.

[0027] Referring now to FIGS. 6 and 7, first actuator 36 and first axis rail 38 slide back and forth in a direction parallel to second axis rail 40 as a force, having a vector parallel to second axis rail 38, is applied to first actuator 36. First actuator 36 includes opening 53 through which second axis rail 40 passes. First actuator 36 includes permanent magnets 54 and 56 that partially, if not completely, surround opening 53. Second axis rail 40 includes conductive coil 58 running lengthwise through its center. Second actuator 37 is than a device capable of causing an electric current to flow though coil 58 in a selected direction. As current flows through coil 58, a magnetic field is generated resulting in a force that urges first actuator 36 and first axis rail 38 to slide in a direction along and parallel to second axis rail 40. Reversing the current through coil 58 urges first actuator 36 and first axis rail 38 to travel in an opposite direction. It is expected that axis rail 40 will be constructed from a material that will allow magnets 54 and 53 to hold first actuator 36 stationary relative to axis rail 40 when no current is running through coil 58.

[0028] A magnetic drive system such as that described above consumes relatively small amounts of energy and can occupy a relatively small amount of space. Other drive systems, however, can be utilized. For example, actuators 36 and 37 may be stepper motors, and axis rails 38 and 40 may be lead screws driven by actuators 36 and 37. When rotated, first axis rail 38—a lead screw urges fluid ejector 10 along the rail's axis of rotation. Similarly, the rotation of second axis rail 40—another lead screw—urges first actuator 36 and first axis rail 38 along an axis of rotation defined by second axis rail 40. Moreover, circuit board 30 may be of such a size and configuration that fluid ejector 10 need only be moved one dimensionally along first axis rail 38. In such cases, the position of first actuator 36 is fixed relative to circuit board 30 while second actuator 37 and second axis rail 40 are unnecessary. In other embodiments a drive subsystem may not be needed at all where fluid ejector 10 can have its position fixed relative to circuit board 30.

[0029]FIG. 8 illustrates the logical programming elements of controller 44 which include coordinate sensor 60, dispenser driver 61, fluid ejector driver 62, and fluid ejector actuator 64. Coordinate sensor 60 represents generally any programming capable of: (1) receiving data representing temperatures sensed by each element of sensor array 42; (2) determining when a temperature sensed by an element exceeds a threshold level; and (3) identifying the coordinates of an area of circuit board 30 sensed by that element. Dispenser driver 61 represents generally any hardware and programming capable of directing dispenser 34 to allow liquid coolant to flow to fluid ejector 10. Fluid ejector actuator 64 represents any programming and hardware capable of energizing fluid ejector 10 causing the ejection of liquid coolant out of fluid ejector 10 and onto circuit board 30.

[0030] Fluid ejector driver 62 represent any hardware and programming capable of directing first and second actuators 36 and 37 to position fluid ejector 10 adjacent to coordinates identified by coordinate sensor 60. Where a magnetic drive subsystem is used as described with reference to FIGS. 4-7, it is expected that an electric pulse passing through coil 52—the pulse having a fixed direction, magnitude, and duration—will cause carriage 46 to move a set and predictable distance and direction along rail 38. Similarly an electric pulse passing through coil 58, the pulse having a fixed direction, magnitude, and duration—will cause carriage 46, first actuator 36 and first axis rail 38 to move a set and predictable distance and direction along second axis rail 40. Where the present positions of carriage 46 and first actuator 36 are known, the number of pulses needed to move carriage 46 and first actuator 36 to particular locations along axis rails 38 and 40 can be calculated.

[0031]FIG. 9 illustrates another embodiment of the present invention in which a cooling system having an array of fluid ejectors 10 is used to cool circuit board 30. Here the cooling system is made up of a number of subsystems including a coolant dispersal subsystem, a temperature sensing subsystem, and a controller. Similar to the embodiment shown in FIG. 3, the coolant dispersal subsystem here includes container 32 and dispenser 34. In this embodiment, however, coolant dispersal subsystem includes manifold 66 and distributors 68. Manifold 66, connected to dispenser 34, represents generally any structure capable of providing a contained liquid coolant flow path from dispenser 34 to distributors 68. Each distributor 68 represents generally any structure capable of providing a contained fluid flow path to a row of fluid ejectors 10.

[0032] While not shown, temperature sensing subsystem includes an array of temperature sensing elements placed adjacent to circuit board 30. Controller 70 represents generally any combination of programming and/or hardware capable of performing the following tasks: (1) receiving data from each temperature sensing element; (2) directing dispenser 34 to allow liquid coolant to flow out through manifold 66, through distributors 68 and on to fluid ejectors 10; and (3) selectively energizing one or more fluid ejectors 10 ejecting liquid coolant onto circuit board 30.

[0033]FIG. 10 illustrates the logical elements of controller 70 which include coordinate sensor 72, dispenser driver 73, and fluid ejector actuator 74. Coordinate sensor 72 represents generally any hardware and programming capable of (1) receiving data representing temperatures sensed by each temperature sensing element; (2) determining when a temperature sensed by an element exceeds a threshold level; and (3) identifying the coordinates of an area of circuit board 30 sensed by that element. Dispenser driver 73 represents generally any hardware and programming capable of directing dispenser 34 to allow liquid coolant to flow to fluid ejectors 10. Fluid ejector actuator 74 represents any programming and hardware capable of identifying and energizing fluid ejector 10 located adjacent to coordinates identified by coordinate sensor 72 causing the ejection of liquid coolant out of the appropriate fluid ejector 10 onto circuit board 30.

[0034] Eventually the contents of container 32 will be depleted. It is expected then that container 32 will be either replaceable or refillable. FIGS. 11 and 12 illustrate container 32 being removed and/or inserted through orifice 76 formed in device 29. Once removed, container 32 can be refilled or disposed. A refilled or new container 32 can then be inserted back into device 29. When inserted into device 29 the container's opening registers with dispenser 34.

[0035] The diagrams of FIGS. 3-12 show the architecture, functionality, and operation of various implementations of the present invention. Other implementations are possible without departing from the scope and spirit of the invention which is defined by the claims following the description. Within the diagrams of FIGS. 8 and 10, each block may represent a module, segment, or portion of code that comprises one or more executable instructions to implement the specified logical functions. Each block may represent a circuit or a number of interconnected circuits to implement the specified logical functions.

[0036] Operation:

[0037] The operation of cooling systems that accord with the present invention will be described with reference to the flow diagrams of FIGS. 13 and 14. FIG. 13 illustrates the operation of a cooling system having a moveable fluid ejector 10—an example of which is shown in the hardware embodiment of FIG. 3. A localized temperature of a surface that exceeds a threshold level is sensed (step 78). The localized temperature corresponds to a portion of the surface to be cooled. The coordinates of the surface portion to be cooled are identified (step 80). Fluid ejector 10 is driven to the identified coordinates (step 82). Fluid ejector 10 is then actuated ejecting liquid coolant onto the portion of the surface to be cooled. (step 84). Liquid coolant is ejected until the sensed temperature falls below the threshold level (step 86).

[0038] Utilizing the particular hardware components illustrated in FIG. 3, the steps of FIG. 13 could be carried out as follows. The elements of sensor array 42 continually send data representing temperature readings to controller 44. Coordinate sensor 60 senses when one of those elements reports a temperature that exceeds a threshold level (step 78). Coordinate sensor 60 then identifies the coordinates of that element within sensor array 42 and, thus, the coordinates of circuit board 30 adjacent to that element (step 80). Using the coordinates identified by coordinate sensor 60, fluid ejector driver 62 directs first and second actuators 36 and 37 to position fluid ejector 10 adjacent to those coordinates (step 82). Dispenser driver 73 directs dispenser 34 to allow liquid coolant to pass from container 32 to fluid ejector 10 while fluid ejector actuator 74 energizes fluid ejector 10 causing liquid coolant to eject on to circuit board 30 (step 84).

[0039] In the meantime coordinate sensor 60 monitors temperature data received from sensor array 42—specifically the temperature data received from the element that reported the high temperature sensed in step 78 (step 86). As long as the temperature reported by that element exceeds the threshold temperature, the process continues with step 84. When the temperature falls below the threshold temperature, the process repeats with step 78.

[0040]FIG. 14 illustrates the operation of a cooling system having an array of fluid ejectors—an example of which is shown in the hardware embodiment of FIG. 9. A localized temperature of a surface that exceeds a threshold level is sensed (step 88). The localized temperature corresponds to a portion of the surface to be cooled. The coordinates of the surface portion to be cooled are identified (step 90). A fluid ejector 10 adjacent to the identified coordinates is identified (step 92). The identified fluid ejector 10 is then actuated ejecting liquid coolant onto the portion of the surface to be cooled. (step 94). Liquid coolant is ejected until the sensed temperature falls below the threshold level (step 96).

[0041] Utilizing the particular hardware components illustrated in FIG. 9, the steps of FIG. 14 could be carried out as follows. The elements of sensor array 42 continually send data representing temperature readings to controller 70. Coordinate sensor 72 senses when one of those elements reports a temperature that exceeds a threshold level (step 88). Coordinate sensor 72 then identifies the coordinates of that element within sensor array 42 and, thus, the coordinates of circuit board 30 adjacent to that element (step 90). Using the coordinates identified by coordinate sensor 72, fluid ejector actuator 74 identifies one or more fluid ejectors 10 located adjacent to those coordinates (step 92). Dispenser driver 73 directs dispenser 34 to allow liquid coolant to pass from container 32 to the identified fluid ejector or ejectors 10 while fluid ejector actuator 74 energizes that fluid ejector or ejectors 10 causing liquid coolant to eject on to circuit board 30 (step 94).

[0042] In the meantime coordinate sensor 72 monitors temperature data received from sensor array 42—specifically the temperature data received from the element that reported the high temperature sensed in step 88 (step 96). As long as the temperature reported by that element exceeds the threshold temperature, the process continues with step 94. When the temperature falls below the threshold temperature, the process repeats with step 88.

[0043] Although the flow charts of FIGS. 13 and 14 each show a specific order of execution, the order of execution may differ from that which is depicted. For example, the order of execution of two or more blocks may be scrambled relative to the order shown. Also, two or more blocks shown in succession may be executed concurrently or with partial concurrence. All such variations are within the scope of the present invention.

[0044] The present invention has been shown and described with reference to the foregoing exemplary embodiments. It is to be understood, however, that other forms, details, and embodiments may be made without departing from the spirit and scope of the invention which is defined in the following claims. 

What is claimed is:
 1. A cooling system, comprising a coolant dispersal subsystem connected to a fluid ejector, the coolant dispersal subsystem operable to supply liquid coolant to the fluid ejector, the fluid ejector placed adjacent to a surface to be cooled and operable to eject the liquid coolant onto the surface.
 2. The system of claim 1, wherein the fluid ejector is a print head.
 3. The system of claim 1, further comprising a drive subsystem operable to selectively move the fluid ejector to a selected location adjacent to the surface.
 4. The system of claim 3, wherein the drive subsystem is operable to move the fluid ejector one dimensionally along a line adjacent to the surface.
 5. The system of claim 4, wherein the drive subsystem is operable to move the fluid ejector two dimensionally across a plane adjacent to the surface.
 6. The system of claim 3, further comprising a control subsystem in communication with a temperature sensing subsystem and the drive subsystem, the temperature sensing subsystem operable to detect localized temperatures of the surface, the control subsystem operable to detect when a localized temperature of an identified portion of the surface exceeds a threshold level and to direct the drive subsystem to position the fluid ejector adjacent to the identified portion of the surface.
 7. The system of claim 6, wherein the control subsystem is further operable to direct the coolant dispersal subsystem to supply the fluid ejector with liquid coolant and to actuate the fluid ejector ejecting the liquid coolant onto the identified portion of the surface.
 8. The system of claim 1, further comprising an array of two or more fluid ejectors each fluid ejector placed adjacent to the surface, wherein the coolant dispersal subsystem is operable to supply each fluid ejector with liquid coolant.
 9. The system of claim 8, further comprising a control subsystem in communication with a temperature sensing subsystem, the coolant dispersal subsystem, and the fluid ejectors, the temperature sensing subsystem operable to detect localized temperatures of the surface, the control subsystem operable to detect when a localized temperature of an identified portion of the surface exceeds a threshold level, to identify a fluid ejector adjacent to the identified portion of the surface, to direct the coolant dispersal subsystem to supply liquid coolant to the identified fluid ejector, and to actuate the identified fluid ejector ejecting the liquid coolant onto the identified portion of the surface.
 10. The system of claim 1, further comprising a control subsystem in communication with a temperature sensing subsystem, the coolant dispersal subsystem, and the fluid ejector, the temperature sensing subsystem operable to detect a temperature of the surface, the control subsystem operable to detect when the temperature exceeds a threshold level, to direct the coolant dispersal subsystem to supply liquid coolant to the fluid ejector, and to energize the fluid ejector ejecting the liquid coolant onto the surface.
 11. A cooling system, comprising: a print head operable to eject a liquid coolant onto a surface to be cooled; a coolant dispersal subsystem operable to supply the print head with liquid coolant; a temperature sensing subsystem operable to detect localized temperatures of the surface; a drive subsystem operable to move the print head to a selected location adjacent to the surface; and a control subsystem in communication with the print head and the drive, temperature sensing, and coolant dispersal subsystems, the control subsystem operable to detect when a localized temperature of an identified portion of the surface exceeds a threshold level, to direct the drive subsystem to position the print head adjacent to the identified portion of the surface, to direct the coolant dispersal subsystem to supply the print head with liquid coolant, and to energize the print head ejecting the liquid coolant onto the identified portion of the surface.
 12. A cooling system, comprising: an array of two or more print heads placed adjacent to a surface to be cooled; a coolant dispersal subsystem operable to supply each print head with liquid coolant; a temperature sensing subsystem operable to detect localized temperatures of the surface; and a control subsystem in communication with the print head and the temperature sensing and coolant dispersal subsystems, the control subsystem operable to detect when a localized temperature of an identified portion of the surface exceeds a threshold level, to identify a print head adjacent to the identified position on the surface, to direct the coolant dispersal subsystem to supply the identified print head with liquid coolant, and to energize the identified print head ejecting the liquid coolant onto the identified portion of the surface.
 13. A cooling system, comprising a means for dispersing a liquid coolant to a means for ejecting the liquid coolant, the means for ejecting liquid coolant being placed adjacent to a surface to be cooled and operable to eject the liquid coolant onto the surface.
 14. A cooling system, comprising: a fluid ejector operable to eject a liquid coolant onto a surface to be cooled; a means for supplying the fluid ejector with liquid coolant; a means for detecting when a localized temperature of the surface exceeds a threshold temperature; a means for moving the fluid ejector to a position that is adjacent to portion of the surface that exceeds a threshold temperature; and a means for actuating the fluid ejector in order to eject liquid coolant.
 15. A cooling system, comprising: an array of two or more fluid ejectors placed adjacent to a surface to be cooled; a means for supplying each fluid ejector with liquid coolant; a means for detecting when a temperature of a portion of the surface exceeds a threshold level; and a means for identifying a fluid ejector that is adjacent to a portion of the surface that has a temperature that exceeds the threshold level; and a means for actuating an identified fluid ejector in order to eject liquid coolant.
 16. A cooling method, comprising: positioning a fluid ejector adjacent to a surface to be cooled; supplying the fluid ejector with a liquid coolant; and actuating the fluid ejector in order to eject the liquid coolant onto the surface.
 17. The method of claim 16, wherein: positioning comprises positioning a print head adjacent to a surface to be cooled; supplying comprises supplying the print head with a liquid coolant; and actuating comprises energizing the print head in order to eject the liquid coolant onto the surface.
 18. The method of claim 16, further comprising identifying when a temperature of the surface exceeds a threshold temperature before actuating the fluid ejector.
 19. The method of claim 16, further comprising identifying a portion of the surface having a temperature that exceeds a threshold temperature, and repositioning the fluid ejector adjacent to the identified portion of the surface.
 20. A cooling method, comprising: positioning an array of two or more fluid ejectors adjacent to a surface to be cooled; supplying the fluid ejectors with a liquid coolant; and actuating at least one of the fluid ejectors in order to eject the liquid coolant onto the surface.
 21. The method of claim 20, wherein: positioning comprises positioning an array of two or more print heads adjacent to a surface to be cooled; supplying comprises supplying the print heads with a liquid coolant; and actuating comprises energizing at least one of the print heads ejecting the liquid coolant onto the surface.
 22. The method of claim 20 further comprising identifying a portion of the surface having a temperature that exceeds a threshold temperature, identifying a fluid ejector that is adjacent to the identified portion of the surface, and wherein supplying comprises supplying the identified fluid ejector with liquid coolant and, actuating, comprises actuating the identified fluid ejector to eject the liquid coolant onto the identified portion of the surface. 